1. Field of the Invention
The present invention relates to a thin film magnetic head including an inductive head for writing, or a combined thin film magnetic head in which an inductive head for writing and a magnetoresistive (MR) head for reading are laminated. More particularly, the invention relates to a thin film magnetic head in which a coil layer can be properly formed and inductance can be reduced at the same time.
2. Description of the Related Art
FIG. 10 is a longitudinal sectional view of a conventional thin film magnetic head, and the left end of the thin film magnetic head in the drawing corresponds to an air bearing surface (ABS).
This thin film magnetic head is provided on the trailing edge of a slider of a floating-type magnetic head which faces a recording medium such as a hard disk, and is a combined thin film magnetic head including an MR head which uses magnetoresistance for reading and an inductive head for writing.
A lower shielding layer 1 is composed of a magnetic material such as an NiFe alloy (permalloy), and a lower gap layer 2 is formed on the lower shielding layer 1. A magnetoresistive element 3 is formed on the lower gap layer 2. The magnetoresistive element 3 includes a multilayer film 4 composed of a spin-valve element (one type of GMR element) or the like that exhibits magnetoresistance, a pair of hard bias layers (not shown in the drawing) formed on both sides of the multilayer film 4, and an electrode layer (not shown in the drawing) for applying a sensing current to the multilayer film 4.
An upper shielding layer 8 composed of a magnetic material such as an NiFe alloy is further formed on the magnetoresistive element 3 with a nonmagnetic upper gap layer 7 therebetween. As described above, the thin film magnetic head shown in FIG. 10 is a combined thin film magnetic head in which an MR head and an inductive head are laminated, and the upper shielding layer 8 also serves as a lower core layer for the inductive head. Hereinafter, the layer represented by numeral 8 is referred to as a lower core layer.
A gap layer 10 composed of a nonmagnetic material, such as Al2O3 (alumina) or SiO2, is formed on the lower core layer 8. An insulating layer 11 composed of a resist material or other organic materials is further formed on the gap layer 10.
A coil layer 12, composed of a conductive material having low electrical resistance, such as Cu, is spirally formed on the insulating layer 11. The coil layer 12 is formed so as to go around a base 15b of an upper core layer 15, which will be described below.
As shown in FIG. 10, the coil layer 12 is covered by an insulating layer 14 composed of an organic material or the like. A hole is made in the gap layer 10 and the insulating layer 14 formed on the lower core layer 8, and the base 15b of the upper core layer 15 is formed through the hole, thus magnetically coupling the upper core layer 15 and the lower core layer 8.
The upper core layer 15 is formed on the insulating layer 14 in the direction of the ABS (toward the left in the drawing), and a tip 15a of the upper core layer 15 is joined to the lower core layer 8 with the gap layer 10 therebetween at the section facing a recording medium to form a magnetic gap having a gap length Gl.
As shown in FIG. 10, above a coil center 12a of the coil layer 12, which is formed at the rear of the lower core layer 8 (on the right side in the drawing), a hole is made in the insulating layer 14, and a coil lead layer 18 is formed on the coil center 12a through the hole.
For example, the coil lead layer 18 is composed of the same material as that for the upper core layer 15, and is formed simultaneously with the upper core layer 15.
In the inductive head for writing, when a recording current is applied to the coil layer 12, a recording magnetic field is induced in the lower core layer 8 and the upper core layer 15, and a magnetic signal is recorded onto a recording medium such as a hard disk by means of a leakage magnetic field from the magnetic gap between the lower core layer 8 and the tip 15a of the upper core layer 15.
However, in the structure of the thin film magnetic head shown in FIG. 10, a sharp step is produced at the rear of the lower core layer 8 (on the right side in the drawing), and the coil layer 12 must be formed on the insulating layer 11 having the step. If the width of the lower core layer 8 (in the track width direction; perpendicularly with respect to the drawing) is smaller than the width of the coil layer 12, a portion of the coil layer 12 in the width direction must be formed on the insulating layer 11 having the step beneath which the lower core layer 8 is not formed.
That is, in the thin film magnetic head shown in FIG. 10, since the lower core layer 8 is not formed entirely beneath the insulating layer 11 on which the coil layer 12 is to be formed, the coil layer 12 extending beyond the lower core layer 8 must be formed on the insulating layer 11 having the step. When the coil layer 12 is formed on such an insulating layer 11 having the step, it is not possible to pattern the coil layer 12 in a proper shape due to inconsistent focus when a resist layer is exposed during the formation of the coil layer 12.
Additionally, by increasing the pitch of the coil layer 12, patterning of the coil layer 12 can be performed properly to a certain extent. However, if the pitch of the coil layer 12 is increased, the length of the upper core layer 15 form the tip 15a to the base 15b must be increased, and thereby the length of a magnetic path made from the upper core layer 15 through the lower core layer 8 is increased, resulting in an increase in inductance.
FIG. 11 is a partial perspective view of a thin film magnetic head which is improved in order to overcome the problems described above, and FIG. 12 is a longitudinal sectional view of the thin film magnetic head shown in FIG. 11.
As shown in FIG. 11, a lower core layer 16 is formed larger than a coil layer 12. Thus, there is no step in an insulating layer 11 in the region in which the coil layer 12 is to be formed (refer to FIG. 12), and the coil layer 12 can be accurately patterned on a planarized surface (the insulating layer 11).
However, as shown in FIG. 11, if the size of the lower core layer 16 is increased, inductance increases, and in particular, in the coming age of high frequency and high recording density, there is a growing need for a reduction of inductance.
As shown in FIG. 12, the lower core layer 16 has a step 16a, following the steps in the individual layers formed thereunder, and it is not possible to form the coil layer 12 on a completely planarized surface (insulating layer 11). When there is such a step 16a, the pitch of the coil layer 12 must be increased so that the patterning accuracy in the formation of the coil layer 12 is improved, and in accordance with the increase in the pitch of the coil layer 12, the length of an upper core layer 15 must be increased, and thus the length of the magnetic path is increased, resulting in a further increase in inductance.
As described above, in the conventional thin film magnetic heads, the formation of a coil layer on a planarized surface without a step and a reduction in inductance are incompatible.